Remove mentions to enable_lock_retries! from docs

Leonardo da Rosarequested to merge
442354/1-remove-enable-lock-retries-usage-from-docs into master

What does this MR do and why?

Remove mentions to enable_lock_retries! from docs.

As enable_lock_retries! It is enabled by default for all migrations, we can remove references to its explicit usage from the database docs.

References #442354 (closed)

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